Porcine pleuropneumonia occurs worldwide and has a high rate of incidence. In Korea, it ranked as the fifth most prevalent porcine bacterial disease in 2009. This disease can affect all age groups and is tended to occur in-between seasons. Pleuropneumonia in pigs is transmitted mainly by airborne route or direct contact with an infected pig. The disease causes considerable economic losses due to increased mortality, growth retardation, and decreased feed efficiency by chronic type, etc. Recently, immune lowering viral diseases in pigs such as porcine Aujesky's disease, porcine reproductive and respiratory syndrome (PRRS), etc. are prevalent and as the scale of farming increases, the disease appears to be increasing in incidence. In addition, porcine pleuropneumonia is a highly contagious disease with sudden onset and short course, leading to mass death in swine. Therefore, there is a dire need to develop a preparation useful in prevention and treatment of porcine pleuropneumonia.
The causative agent of porcine pleuropneumonia is Actinobacillus pleuropneumoniae. The pathogens of this bacterium are known as polysaccharides, lipopolysaccharide, hemolysin, enterotoxin, IgA protease, bacterial outer membrane protein, etc. Sixteen serotypes are reported and twelve have been described. Serotypes 2 and 5 are most commonly isolated in Korea.
There exists a need to develop an appropriate alternative therapeutic agent for pleuropneumonia in pigs.
Recently, a bacteriophage is being magnified as an alternative to treat bacterial diseases. Due to the preference for eco-friendly methods, use of bacteriophage is of a higher interest than ever. A bacteriophage, or “phage”, is a very tiny microorganism that infects bacteria. Bacteriophages kill bacteria by entering bacterial host cells and replicating. When enough phage offspring are produced host cells will be broken open and die. The phage offspring spill out of the cell and diffuse toward new hosts. Due to its very high specificity, the bacteriophage capable of infecting a specific bacterium is very limited in type. Namely, a specific bacteriophage can infect and kill only specific bacteria while affecting no other bacteria.
Bacteriophage was first found by British bacteriologist Twort in 1915 during his research on the phenomenon that micrococcus colony turns opaque somehow. Independently, French bacteriologist d'Hérelle discovered a microbe that decomposes Shigella disentriae in a filtrate of feces of a patient with dysentery and called the microbe a bacteriophage or bacteria-eater. Since then, bacteriophages against Shigella dysenteriae, Salmonella Typhi, and Vibrio cholerae were further identified.
After the discovery of bacteriophages, a great deal of faith was placed in their use due to their special ability to kill bacteria and many researches were conducted. With the advent of penicillin that was found by Flemming in 1941, antibiotics became popular and widely marketed. Hence, the study of bacteriophages was largely abandoned in the West except for some East European countries. However, limitations of conventional antibiotics due to antibiotic resistance that have been reported since 2000 have led to a resurgence of interest in bacteriophage as an alternative to antibiotics.